1. Field of the Invention
The present invention relates to the power transformer and more particularly to planar transformers field and power transformer structures, which involves the power transformer and different magnetic elements.
2. Description of the Related Art
In order to comply with the height requirements for power transformers the conventional barrel transformer have been replaced by planar structures. The planar structures consists in staking up layers composed by dielectric sheet and copper spirals interconnected through pins penetrating through holes in the dielectric sheets. In application wherein compliance with safety agencies is required which demands that a high voltage level has to be sustain in between primary winding and secondary winding a bobbin 37a and 37b may be employed as depicted in FIG. 3. In between he the dialectic layers such as 31a, there are spiral of copper material interconnected through interconnection holes such as 150, and interconnection pins. This method is labor intensive, requires a special bobbin and interconnection pins which are mechanical unreliable.
Another methodology is locating the winding within a multilayers PCB. Each layer of the multilayer PCB contains one or more spiral turns, which are interconnected using, metalized via. This method of construction is simple and reliable. It does not address the high power requirements. In order to process high current the copper thickness has to be high or the number of layers have to increased. Both solutions are very costly. The concept presented in this invention is combining the multilayer PCB construction for one of the transformer winding which process low current, with copper strips attached to the multilayer PCB using metalized holes for positioning and interconnection. The metalized via for positioning allow the use of soldering attachment. The multilayer PCB wherein the low current winding implemented offers the mechanical support for the secondary copper strips and the required insulation between the primary and secondary. Power connector may be further attached to the multilayer PCB for a better interface to the rest of the circuit. Another advantage of this technology is the fact that additional inductive elements can be implemented on the same multilayer PCB. Another advantage is the fact that multiple magnetic cores can be used on the same multilayer structure wherein the primary winding is embedded. These multiple transformer elements can have the primary in series or in parallel to ensure a uniform utilization of all the magnetic cores. Additional pads can be placed on the multilayer PCB to accommodate surface mounted components. Some of the layers of the multilayer PCB can be utilized for different function such as shielding or noise cancellation. In some of the embodiments of the invention the secondary winding can be also implemented in multilayer PCB technology. In this way we can have multiple turns for the secondary.